A posterior subtenon injection of triamcinolone acetonide is an alternative to intravitreal injection in diabetic macular edema and is known to have fewer vision-threatening complications. Here, we report a case of periocular abscess following posterior subtenon injection of triamcinolone. A 62-year-old woman who had diabetic macular edema and disc neovascularization underwent a posterior subtenon injection of triamcinolone acetonide and panretinal laser photocoagulation. One month later a periocular abscess was noted in the inferotemporal area adjacent to the scleral wall. Pus was removed by fine-needle aspiration, and microbiologic cultures identified Pseudallescheria boydii. The patient was given systemic and subconjunctival treatment with itraconazole. However, conjunctival infection and anterior chamber inflammation worsened, and another posterior subtenon abscess was found. Despite long-term systemic and topical itraconazole therapy, retinal detachment and vitreous opacity were shown on B-scan, and atrophic bulbi resulted. Pseudallescheria boydii infection of the eye and orbit can result in a poor visual outcome. Prompt surgical debridement and drainage of the abscess, along with appropriate antifungal therapy based on susceptibility testing, must be mandatory.